<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .a {
            width: 100px;
            height: 100px;
            background-color: #f00;

            /* position: absolute;   脱离 */


            /* 不脱离的 ，正常占位置 */
            position: relative;
            /* 相对于自身位置而言的 , 且只保留原来的位置*/
            left: 30px;
            top: 50px;
            /* margin-top: 50px; */

            z-index: 3;
        }

        .b {
            width: 100px;
            height: 100px;
            background-color: #ff0;

            position: relative;
        }
    </style>
</head>

<body>

    <div class="a"></div>
    <div class="b">啊啊啊啊啊啊啊啊啊啊啊啊</div>


</body>

</html>